I already posted this Q in my introduction thread and I hate to ask twice but, maybe if the answer is here, it can help anyone else who ends up with my same questions:

Should I connect to my head unit's 2.5v RCA sub outs or tap into my speaker channels? If I use my sub out, I can use the low-pass filter in my HU to block the bass frequencies to my factory speakers. But, I see the recommendations in the FAST-9999 thread to always use the high-level inputs instead. My HU claims it puts out 20 watts RMS x4 channels at 4 ohms.

I'm not sure which is considered the high-level input for this tube. And, if the RCA's are the lower choice, would it be worth it, to use the bass filter in my head unit?

Thanks again. (^_~)

Take advantage of the subwoofer output of the headunit.

The High Level Input is quite simply connecting to the speaker outputs of the headunit. The voltage level is high, thus, High Level Input.